Evaluating the molecular composition of total dissolved organic matter in Baffin Bay using novel proton (1H) nuclear magnetic resonance (NMR) spectroscopy water suppression method
Kayla McKee, Brett D. Walker
Department of Earth and Environmental Sciences, University of Ottawa
Kayla McKee, Brett D. Walker
Department of Earth and Environmental Sciences, University of Ottawa
Marine dissolved organic matter (DOM) is the largest reduced pool of actively cycling carbon in the oceans. Despite the importance of DOM for the ocean carbon and nitrogen cycles, we lack a detailed understanding of the molecular composition of DOM. The composition of DOM is especially important in determining its biological cycling within the rapidly changing Arctic ocean. Due to the high concentration of salts in seawater, typically chemical- or size fractionation methods are used to isolate enough DOM in order to characterize the DOM compound classes either isotopically or compositionally. These methods bias the compound classes that are being observed however, because one can only observe a small fraction of the DOM pool. Thus, if one wants to look at the total DOM composition of a sample, one cannot do so with these fractionation methods. There is a need, in this area of research, to ascertain the unbiased composition of the total DOM pool in seawater; however, to date, this has not been possible. Here we present the molecular composition of total seawater DOM from Baffin Bay, via the use of a novel proton nuclear magnetic resonance (1H-NMR) spectroscopy water suppression technique for aqueous organic samples. Specifically, the composition of key DOM functional groups (CH3-deoxysugars, CHO-carbohydrates, N-acetyl amino sugars, methanethiol, and CRAM) was determined for the depth profile (n=15) of the deepest station (BB2) in the center of Baffin Bay, and for surface water samples for all 11 sampled stations. DOM composition changes were reported as a function of depth and location in the bay. It was concluded that as both the Western Greenland Current (WGC) and the Baffin Island Current (BIC) travel along their respective coastlines, the percent relative abundance of CH3-deoxysugar, N-acetyl amino sugar, and methanethiol increases, and CHO-carbohydrates decreases. It was also determined that the percent relative abundance of carboxyl-rich alicyclic molecules (CRAM) increases with depth and CHO-carbohydrate simultaneously decreases with depth; this pattern occurred until the benthic zone was reached, at which point the CRAM abundance dropped and the CHO-carbohydrate abundance suddenly increased. These data will be discussed in the context of unique DOM sources (advected, autotrophic, glacial, sea-ice) and microbial recycling of DOM with water mass advection. Overall, this research will provide a better understanding of the composition and cycling of DOM in the Canadian Arctic.